The invention relates to the construction of a rectifier device for the three-phase dynamo of a motor vehicle. According to the classic principle of the three-phase dynamo, three equal, mutually independent coils u, v, w are present which are arranged with mutual interspacings of 120xc2x0 (stator). The excitation coil is present on the rotary part on the inside (rotor). The moment an excitation current flows through the coils, a magnetic field will arise which in its turn induces a three-phase AC voltage in the stator coils, which supplies the three-phase current when a load is connected. This current is rectified by means of a bridge rectifier circuit and serves to supply the loads and to charge the battery. The output voltage of the dynamo is controlled by a control unit (pulse width modulation of the excitation current, PWM), i.e. the average value of the excitation current is set in dependence on the instantaneously obtaining battery voltage.
Known electrical rectifier devices for motor vehicle applications are built up with diodes having special housings which are mechanically pressed in into metal cooling plates (so-called press-fit diodes), or which are soldered onto cooling plates. The construction of the electrical and thermal connection between the diodes and the cooling body (usually a cooling plate serving as a carrier for the components) is of special importance because the power losses in the relevant components must be removed sufficiently quickly in view of the high electrical current values (typically approximately 50 A up to 130 A) in the diodes. The mechanical interconnections of the (usually eight) diodes and the electrical connection points are usually formed by a metal pressed screen molded around with synthetic resin.
To realize a rectifier of the construction described above, diodes for the various half waves are mounted on separate cooling plates. The complete assembly then results in a rectifier device in which diodes at different levels are interconnected by complicated conductor configurations. This typeof assembly requires considerable expenditure and comprises many separate manufacturing steps. In addition, mechanical processes are required, such as riveting, screwing and spot welding, which are not ideal for the electrical components.
It is an object of the invention accordingly to provide a rectifier device for three-phase dynamos which has improved properties as regards its manufacturing technology.
This object is achieved with a rectifier device, having a cooling body, for a three-phase dynamo of a motor vehicle comprising a cooling body, comprising at least one circuit carrier arranged on the cooling body and having an electrically conductive structure on its surface, comprising at least a first diode arranged on the surface of a circuit carrier with an electrically conductive structure and designed for rectifying a first half wave, and comprising at least a second diode arranged on the cooling body and designed for rectifying a second half wave. The rectifier device according to the invention utilizes the modular construction method of power electronics technology for realizing a rectifier for a three-phase dynamo which renders possible a compact and simplified assembly. Naked semiconductor diode chips (i.e. without housings) are joined together into a rectifier device above a power substrate (for example, a direct bonded copper or DBC substrate) provided on a cooling body. All diodes are in one plane here and electronic manufacturing processes such as, for example, automatic component placement, SMD soldering, and wire bonding can be used. This means that the manufacture can take place on normal installations for electronic manufacture without specially designed machines. The constructive incorporation of the semiconductor diodes of the rectifier into the overall assembly is given most attention here. In general, however, the invention may be used for all applications with power semiconductors.
The thermal resistance of the rectifier device described above can achieve substantially lower values than is the case in conventional solutions. Construction and connection technologies are known from electronics manufacture. The rectifier device can be given smaller dimensions because of its construction and the low thermal resistance compared with traditional solutions. The module with a cooling plate is highly suitable for water-cooled three-phase dynamos.
An embodiment of the invention will be explained in more detail below with reference to drawings, in which